The present invention relates to a method and a device for controlling an internal combustion engine.
Such a method and such a device for controlling an internal combustion engine are known from the German Published Patent Application No. 195 27 218. There, a method and a device are described for controlling the smooth running of an internal combustion engine. A manipulated variable can be preset on the basis of at least one measured quantity, which here is the speed of the internal combustion engine. To form the manipulated variable, the measured quantity is filtered by at least one filter means. Usually in the case of a smooth-running control, each cylinder of the internal combustion engine is assigned a control which, as a function of a system deviation allocated to it, forms a manipulated variable for the cylinder assigned to it. The system deviation is derived from the actual values and setpoint values allocated to the individual cylinders. The time intervals between two combustions or the duration of at least one segment, which is defined by a segmental wheel, are used as the actual value. The setpoint values are preferably yielded by an averaging using all actual values.
The spacing between two pulses on a so-called segmental wheel is usually designated as a segment. In this context, the interval between two combustions is generally divided into two segments. The segmental wheel can be placed on the camshaft or the crankshaft and delivers two pulses per combustion process. Alternatively, the segment pulses can also be generated on the basis of other signals.
The actual and setpoint values are preferably ascertained in a frequency-specific manner, i.e. the output signal of the speed sensor is filtered by band-pass filters, and the actual and setpoint values for a frequency are formed on the basis of this filtered signal. Provision is made to weight the amplification of the band-passes and/or the frequency-specific system deviation. These weighting factors are usually stipulated within the framework of the application. It is also provided that, to form the frequency-specific actual values for different frequencies and different vehicle types, different segments are selected which take into account the frequency-specific and vehicle-specific phase shifts between quantity oscillation and rotational-speed oscillation. Therefore, it is likewise established within the framework of the application, which segments are utilized for actual value formation and/or setpoint value formation.
Due to this stipulation of the segment selection and of the band-pass amplification, a considerable outlay results in the application.
Using the procedure of the present invention, the outlay can be markedly reduced in the application. In particular, the time expenditure and the requirement for measuring technology can be reduced, since no external measuring instruments are necessary.
Because an excitation variable is superimposed on the manipulated variable, and because properties of the filter means are determined on the basis of the resulting reaction of the measured quantity, the properties of the filter means can be adapted individually to the respective vehicle.
According to the present invention, the properties of the filter means are determined in preferred operating states. The determination is preferentially carried out at the end of the vehicle manufacture and/or within the framework of servicing the vehicle. Thus, the properties can be optimally selected over the entire service life of the vehicle.
It is particularly advantageous if the filter means are constructed as a band-pass filter with adjustable amplification. In this case, the band-pass amplification is adapted.
If the filter means ascertains an actual value and/or a setpoint value by evaluating specific rotational-speed segments, then this segment selection is designated as a property of the filter means.
The amplification and the segment selection determine the properties of a smooth-running control. The performance of the vehicle can be favorably influenced by a precise adaptation of these variables to the respective vehicle.
It is particularly advantageous if a periodic variable is used as excitation variable whose frequency corresponds to the crankshaft frequency, the camshaft frequency and/or an integral multiple of these frequencies. These frequencies correspond to the disturbances generally occurring.